In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, with each service area or cell area being served by a radio network node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” or “eNodeB”. The service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node operates on radio frequencies to communicate over an air interface with the wireless devices within range of the access node. The radio network node communicates over a downlink (DL) to the wireless device and the wireless device communicates over an uplink (UL) to the radio network node.
A Universal Mobile Telecommunications System (UMTS) is a third generation telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for communication with user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for present and future networks e.g. UTRAN, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. The RNCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS) have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases for e.g. 4th and 5th generation networks. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a 3GPP radio access technology wherein the access nodes are directly connected to the EPC core network. As such, the Radio Access Network (RAN) of an EPS has an essentially “flat” architecture comprising access nodes connected directly to one or more core networks.
The 3GPP is currently working on standardization of the 5th generation (5G) of radio access system, also called New Radio (NR) network. An evolved architecture for the RAN is foreseen, both for the LTE Evolution and the New Radio tracks of 5G. This includes a solution where the radio network nodes such as radio base stations may be split into parts for radio network control, packet processing and radio nodes (RN) with base-band processing and radio units. An example of the new architecture is shown in FIG. 1, indicating possible interfaces and also Radio Control Nodes (RCN) and Packet Processing Node (PPN).
The NR network need to be connected to some core network that provides non-access stratum (NAS) functions and connection to communication networks outside NR, like the internet. This is here shown as a core network as specified by 3GPP.
Existing solutions rely on frequent broadcast of cell identities and other radio area identities from all radio nodes all the time. These identities can then quickly be read by wireless devices in the wireless communication network and be reported to a serving radio network node such as a RCN or RN. The serving radio network node can then identify neighbour cells and radio network nodes.
A proposed solution for downlink based active mode mobility in NR is depicted in FIG. 2. A wireless device is served by the leftmost radio network node but is traveling in the direction towards the rightmost radio network node, depicted by the dashed arrow in the FIG. 2. The wireless device uses a best “home MRS”, from the serving radio network node, for coarse timing estimation and radio link quality monitoring and failure detection.
In addition, the wireless device monitors a sparse periodic Mobility Reference Signal (MRS) from the serving radio network node and compares it with similar periodic and sparse MRSs from potential target radio network nodes. When a target radio network node becomes relevant for a more detailed handover procedure additional dynamically configured home MRSs and dynamically configured away MRSs may be activated.
The final handover decision is taken by e.g. the serving radio network node and it is based on wireless device reports containing measurement of home MRSs and away MRSs.
An example embodiment of the proposed system information acquisition for 5G NR is depicted in FIG. 3. In the example each radio network node, such as a Transmission/Reception Point (TRP) or a radio base station e.g. an eNB or gNB, transmits a synchronization signals or a system signature signal (SS). Together with the SS each radio network node also transmits a physical broadcast channel (PBCH) containing some of the minimum system information that the wireless device needs to access the wireless communication network. This part of the minimum system information is denoted as master information block (MIB) in the FIG. 3. In the left oval a SS1 and a MIB1 transmission is used and in the right oval a SS2 and a MIB2 transmission is used. A transition of SSs and the PBCH containing the MIBs is the overlapping part of the ovals.
By reading the MIB the wireless device receives information on how to receive a system information block (SIB) table. The SIB table may be transmitted using a broadcast format such as single frequency network (SFN) transmission and is transmitted over both the ovals. In addition to the minimum system information that is periodically broadcasted in by the SS+MIB and in the SIB-table the wireless device may receive other or additional system information e.g. by a dedicated transmission after initial access is established, depicted as a narrow beam from the right radio network node.
In order for the proposed active mode mobility solution depicted in FIG. 2 to work the serving radio network node needs to know the identity of the neighbouring radio network nodes. If a wireless device reports an away MRS then the serving radio network node needs to know which neighbouring radio network node that is transmitting the MRS.
If the wireless device reports an unknown away MRS then the automatic neighbour relation (ANR) algorithm is supposed to identify the source of the MRS and set up a neighbour relation. In LTE this is done by requesting the wireless device to read the cell global identity (CGI) associated with the measurement and report this global identity to the serving radio network node. The serving radio network node then contacts a server in the wireless communication network and receives an IP-address of the radio network node with said CGI and initiates a neighbour relation setup procedure.
In NR, which is designed to support high gain and dynamic beamforming, e.g. by means of utilizing hundreds of antenna elements at the base station, so called massive Multiple Input Multiple Output (MIMO), this solution may not work. This is depicted in FIG. 4.
In NR a typical situation is that a wireless device reports an unknown “away MRS” but then it cannot read any system information, such as the SS+MIB, of the corresponding radio network node. Therefore, even if we would transmit a CGI in the MIB in NR the ANR algorithm may still fail.
A procedure of “release and redirect” in which the wireless device is released from the serving radio network node with an instruction to connect to the new unknown radio network node and inform the new unknown radio network node about the CGI of the old source radio network node such that the new radio network node may initiate the ANR establishment has been discussed as a solution to this problem. But, as depicted in FIG. 4 it is possible that the wireless device may hear another SS+MIB, dashed transmission of SS2 in the FIG. 4, but it is the wrong one.
If ANR does not work, then the network cannot figure out what an MRS comparison means and a handover cannot be performed, e.g. move the wireless device context, re-direct backhaul traffic, assign contention free PRACH, etc, in time.
Figuring out the SS associated with a particular MRS does not help much since the SS identity (SSI) is not globally unique. We have just moved the problem from the MRS-domain to the SSI-domain. Many nodes in the network transmit SS3 and the radio network node does not know which radio network node sent the SS3. Without a working ANR solution for NR, the active mode mobility solution does not work which leads to a reduced or limited performance of the wireless communication network.